1. Technical Field
The present invention relates to fingerprint detection devices, and more particularly to electronic fingerprint detection devices for sensing the unique surface topography of a fingerprint.
2. Discussion
Fingerprint detection devices are utilized in many applications requiring an extremely high probability of positive recognition of persons seeking access to secured areas, at customs and border inspections, and where it is essential to verify that the correct person is involved in the transaction. Other forms of identification have been implemented to verify the correctness of a specific person including photographic identification, signature verification, and personal identification numbers (PIN). Problematically, the latter of these schemes fail to uniquely identify an individual with the same level of assurance as an individual's fingerprints. All of the above-mentioned forms of identification are extremely susceptible to fraudulent modification. The likelihood of two sets of fingerprints being the same is so remote that law enforcement agencies use fingerprints with high confidence to positively identify individuals. Real time fingerprint detection devices have been implemented for high probability identification, but many limitations still exist. The associated costs currently make large scale distribution of these devices impossible.
Currently, fingerprint detection devices employ some form of imaging system to scan the unique characteristics of a fingerprint which are then compared to those same characteristics of a known reference fingerprint. Typically these imaging systems consist of thermal or optical sensors for translating fingerprint line information into digital wave forms that can be analyzed by a microprocessor. Further, these imaging components require complex optics, lasers or electronic circuits which are expensive to manufacture. Therefore the devices in which they operate are expensive and typically have limited portability. They also require complex image processors to implement the fingerprint detection algorithms. To operate these conventional devices, the fingerprint is placed upon the imaging surface, and remains stationary while the device electronically scans or optically images the fingerprint line characteristic information. This often involves arrays as large as 256.times.512 sensing elements making the integrated sensor expensive and vulnerable since it must come in contact with the finger. These complex arrays produce a large number of data points that must be processed and ultimately stored for reference. In addition they are highly susceptible to dirt and oils contained within their operating environment. Some arrays also require a complicated registration system for detecting the position or relative center of the fingerprint and establishing reference points before scanning the fingertip and processing its characteristics against a known reference.
An exemplary approach is disclosed in U.S. Pat. No. 4,582,985 to Lofberg entitled "Data Carrier" which discloses a fingerprint verification system fabricated into a device approximately the size of a credit card. The device includes a memory used to store a previously obtained reference bit sequence. The fingerprint to be detected is placed upon an imaging device consisting of thermal or optical sensing elements for translating fingerprint line information into a digital bit sequence. The digital signal is then compared to a reference bit sequence by a microprocessor. If the comparison process achieves a match within a certain degree of coincidence, a positive detection signal is produced. However, as noted above, this approach accomplishes fingerprint verification by using a sensing array with a large number of sensing elements. This complex array is expensive to fabricate, produces large volumes of data to process, and is easily damaged by excessive force. It further requires a registration means for detecting the position of the stationary fingertip, thereby increasing the complexity of the circuitry and requiring additional data processing capabilities.
Thus it would be desirable to provide a fingerprint detector employing a sensing array with a small number of sensing elements, thereby simplifying the data processing requirements by reducing the quantity of data to be analyzed and lowering overall power consumption permitting battery operated devices. In addition, it would be desirable to provide a fingerprint detection device which utilizes an electronic sensor allowing the electronics to be implemented within a single integrated circuit to reduce cost and eliminate exotic imaging technologies. These features enable manufacturing a cost effective device for large scale implementation in both industrial and consumer applications. Furthermore, it is desirable to provide a sensor which produces an electronic signal with high signal-to-noise ratio and high dynamic range, thereby significantly reducing the probability of error.